Liquid Analysis Apparatus

ABSTRACT

A rotary analytical device for use with a reagent cartridge. The cartridge may have a housing, an axis, analysis chambers spaced from and located circumferentially about the axis, and a magnetically movable element located in and movable within each analysis chamber to mix fluid in the analysis chamber. The rotary analytical device may have a housing with a cavity having an axis, an impeller extending into the cavity and rotatable about the axis to receive and rotate the cartridge, a motor to rotate the impeller, at least one magnetic element near the cavity and offset from the axis, a light source in the housing to direct a beam of light into the cavity and through the analysis chamber of the cartridge, and a light sensor to receive light from the analysis chamber.

RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.13/611,843, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

It is frequently desired to analyze a liquid to determine the presenceand concentration of analytes such as minor constituents and/orcontaminants. In many instances, several different tests may be run onone or more portions of a single liquid sample, to detect and measuredifferent constituents. For many common tests, reagents are availablethat provide an almost instantaneous result by changing either hue orintensity of color in response to a specific constituent in the liquid.An example is a swimming-pool test kit, which typically provides fromtwo to six different reagents that test for common factors such aschlorine or bromine content, pH, and hardness of the water.

However, such test kits conventionally require the user to fill aspecific amount of water into a test container, add a specific amount ofreagent, judge the intensity or hue of the resulting color against areference chart by eye, and repeat the whole process for each test thatit is desired to carry out. If the test results are not within a desiredrange, the user must then manually calculate the amounts of chemicals toadd to the swimming pool to adjust its condition to the desired range.That is time consuming, messy, and not very accurate. The situation iseven worse for a pool supply store, where the store staff are frequentlyasked for assistance by a pool owner whose pool chemistry has gone wrongin a way that the owner cannot himself correct. The store staff may thenneed to conduct a much larger range of tests, and to convert the resultsof the tests to quantities of various chemicals to be added to the pool.

Similar issues occur in other businesses and industries. For example, inbrewing, trace constituents of the water used can not only directlyaffect the flavor and quality of the brewed beverage, but also affectthe behavior of the yeast and therefore the success and result of thebrewing process. Other businesses in which a battery of tests have to beperformed fairly frequently, so that similar issues occur, includeaquaria, aquaculture, environmental monitoring, and maintaining boilersand coolers.

There is, therefore, a need for apparatus and methods that make itpossible to test a liquid sample for several different properties, forexample, for the presence or absence of several different analytes, in asingle operation, with a minimum of mess, and to obtain the results ofthe tests automatically, without relying on human judgment.

SUMMARY OF THE INVENTION

One embodiment of the invention provides a rotary analytical devicecomprising a housing having a cavity formed therein, the cavity beingdefined by a bottom wall and at least one side wall, the cavity havingan axis, an impeller extending into the cavity and rotatable about theaxis, a motor mounted within the housing and connected to the impeller,the motor adapted to rotate the impeller, at least one magnetic elementin the housing at a location proximate to the cavity and offset from theaxis, at least one light source in the housing and arranged to direct abeam of light into the cavity, and at least one light sensor in thehousing and arranged to receive light from the at least one lightsource, the sensor being sensitive to light of a color emitted by thelight source.

Further embodiments of the invention provide combinations of a rotaryanalytical device and an analytical cartridge co-operating with therotary analytical device, and methods of analysis using such rotaryanalytical devices, such analytical cartridges, and such combinations ofa rotary analytical device and an analytical cartridge.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention may be more apparent from the following more particulardescription of embodiments thereof, presented in conjunction with thefollowing drawings. In the drawings:

FIG. 1 is a schematic view of an embodiment of a liquid analysisapparatus.

FIG. 2 is a perspective view of a rotary analyzer forming part of theliquid analysis apparatus of FIG. 1.

FIG. 3 is a top plan view of a cartridge used in the rotary analyzer ofFIG. 2.

FIG. 3A is a cross-section view of an analysis chamber and agitatorchamber.

FIG. 3B is a view similar to FIG. 3A in a different position inoperation.

FIG. 4 is a view similar to FIG. 3A of an alternative embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A better understanding of various features and advantages of the presentmethods and devices may be obtained by reference to the followingdetailed description of illustrative embodiments of the invention andaccompanying drawings. Although these drawings depict embodiments of thecontemplated methods and devices, they should not be construed asforeclosing alternative or equivalent embodiments apparent to those ofordinary skill in the subject art.

Referring to the drawings, and initially to FIG. 1, one form of liquidanalysis apparatus, indicated generally by the reference number 10,comprises a rotary analyzer, indicated generally by the reference number12 and shown in more detail in FIG. 2, connected to a computer 14.Computer 14 may be a conventional personal computer or similar devicesuitably programmed, and may comprise, among other equipment, aprocessor or controller 16, input and output devices such as a keyboard18 and a monitor 20, random access memory (RAM) 22, read-only memory(ROM) 24, magnetic disks or other long-term storage 26, and an interface28 to an external network 30 or other communications media. Theinterface 28 may also provide a connection from the computer 14 to therotary analyzer 12.

Referring now also to FIG. 2, the rotary analyzer 12 comprises a base 50defining a recess 52 in its upper surface, and a lid 54 hinged to base50 and defining a generally cylindrical recess 56 in its lower surface.When the lid 54 is closed, it preferably fits into recess 52. A spindle58 projects through the lower surface of the recess 52 and is receivedin the recess 56 when the lid 54 is closed. The spindle 58 has a flatsurface 60 on one side. Below the bottom of the recess 52, the spindle58 is connected to and driven by a motor 62, and is preferably connectedto a rotary encoder 64 or similar device by which its rotationalposition can be monitored. However, as will become apparent after reviewof the following description, other well known mechanisms can be used toprovide rotational position signals to the apparatus.

In the embodiment shown, four light sources, preferably light emittingdiodes (LEDs) 68, 70, 72, 74 are mounted in the underside of the lid 54in the top of recess 56. The LEDs 68, 70, 72, 74 may be of differentcolors, for example, respectively red, yellow, green, and blue. Fourlight detectors, such as photodiodes or other photoelectric transducers76, 78, 80, 82, are mounted in the bottom of the recess 52, each facinga respective one of LEDs 68, 70, 72, 74. Each transducer 76, 78, 80, 82may be provided with a dichroic or other band-pass filter or otherwiseoptimized to be selectively sensitive to the light from its respectiveLED. It is also contemplated that the light sources could be located onthe same side as the detectors (e.g., the bottom of the recess) with areflective surface mounted on the opposite side of the recess (e.g., onthe lid).

In other embodiments, more or fewer light sources, and/or light sourcesof different colors, which may include infrared and/or ultraviolet, maybe used. In other embodiments, other sorts of light sources, which mayinclude a broadband source such as an incandescent lamp, may be used.

A first permanent magnet 84 is mounted in the underside of lid 54between two of the LEDs. A second permanent magnet 86 is preferablymounted in the bottom of recess 52, between two of the transducers,spaced apart from the first magnet 84. The LEDs 68, 70, 72, 74, thetransducers 76, 78, 80, 82, and the magnets 84, 86 are preferably all atthe same radius from the axis of rotation of spindle 58, however it iscontemplated that the magnets can be located at a different radiusdepending on the construction of the cartridge.

An indicator lamp 88 may be provided on the exterior of the rotaryanalyzer 14, in a position where it is easily visible even with lid 54closed. An interlock switch 90 may be provided to detect when lid 54 isclosed.

A processor or controller 94 suitably programmed is provided, andreceives inputs from the transducers 76, 78, 80, 82, the rotary encoder64, and interlock switch 90, and controls the LEDs 68, 70, 72, 74, themotor 62, and the indicator light 88. The interlock switch 90 ispreferably configured to provide signal to the processor or controller94 for detecting when the lid is closed in order to prevent activationof the spindle 58 when the lid is not in its closed position. Theindicator light 88 preferably is illuminated when the analyzer is activeor when the testing is complete.

Referring now also to FIG. 3, one form of cartridge, indicated generallyby the reference number 100, comprises a molded body with a generallyflat lid or top surface 101. Cartridge 100 comprises a central opening102 that is preferably D-shaped an configured to engage with the flat 60on the spindle 58, so that when the cartridge 100 is mounted on thespindle 58 the orientation of the cartridge 100 relative to the rotaryencoder 64 is fixed and predetermined. It is contemplated that theopening 102 can be any suitable non-circular shape designed to mate witha complementary spindle shape.

At least partially surrounding the central opening 102 is an annularfilling chamber 104, which in one embodiment extends around the openingabout 330° of the circumference of the cartridge. At one end of thefilling chamber 104 preferably includes a radially inward extension 106,that includes a filling port 108, which is the an opening through thelid of cartridge 100. Water can be injected through filling port 108using a conventional syringe (not shown) into filling chamber 104.Visible indicia may be molded into or placed on the lid of the cartridge100, for example, to point out where the filling port 108 is locatedand/or to indicate a point to which the filling chamber 104 should befilled.

At the end of the filling chamber 104 remote from the filling port 108,a transfer passage 110 extends radially outward to a distributiongallery 112, which in the illustrated embodiment almost completelyencircles the cartridge 100 outside the filling chamber 100. Of courseit is contemplated that multiple passages 100 can communicate withmultiple galleys 112. From the distribution gallery 112, a plurality ofspouts or channels 114 extend radially outward. From the end of thedistribution gallery 112 furthest from the transfer passage 110, thereis preferably located an overflow passage 116 that extends radiallyinwards, and opens into the central opening 102 through the flat side ofthe D-shaped opening.

Outside the distribution gallery 112 are several analysis chambers 120,each with an associated agitator chamber 122, at least one comparisonchamber 124, and an overflow chamber 126. The analysis chambers 120,comparison chamber 124 and overflow chamber 126 are each connected tothe distribution galley through one of the channels 114. The analysischambers 120 are located circumferentially on a circle with a radiusthat corresponds to the radial location of the LEDs 68, 70, 72, 74, thephotoelectric transducers 76, 78, 80, 82, and preferably the magnets 84,86. The analysis chambers 120 are preferably equally sized and evenlyspaced, although that is not necessary in the present invention. In thecartridge 100 shown in FIG. 3, there are ten analysis chambers 120,spaced at intervals of approximately 30° ( 1/12 of the circumference ofthe cartridge). The comparison chamber 124 occupies an eleventhposition, and in the illustrated embodiment is about the same size as ananalysis chamber, but does not have an associated agitator chamber. Theoverflow chamber 126 occupies the twelfth position, and is larger thanthe analysis chambers. The overflow chamber 126 uses up the space thatis available where the overflow and comparison chambers do not haveagitator chambers. The overflow chamber 126 is at the same end ofdistribution gallery 112 as the overflow passage 116.

As shown in FIG. 3A, the analysis chambers 120 are elongated in thecircumferential direction, and extend between the top and bottom of thecartridge 100, closed off by the lid 101. The agitator chambers 122 arepreferably generally circular in cross-section, and extend between thetop and bottom of the cartridge 100, closed off by the lid 101. Eachagitator chamber 122 is connected to its associated analysis chamber 120by a slot 128 preferably extending between the top and bottom of thecartridge. Each agitator chamber 122 contains an agitator 130 preferablyin the form of a magnetizable stainless steel ball hearing (BB) that issmall enough to move freely along the agitator chamber 122 between thepositions shown in FIG. 3A and FIG. 3B, but large enough to displacewater like a piston when it does so, and too large to pass through theslot 128.

The top and bottom faces or surfaces of the cartridge 100 above andbelow the analysis chambers 120 are preferably made smooth, flat, andclear, so as to permit the transmission of light with minimal absorptionand scattering.

In a ready-for-use condition of the cartridge 100, each analysis chamber120 contains a predetermined amount of a selected reagent 121.Preferably, the reagents 121 are introduced into the analysis chambers120 in liquid form and dried or allowed to dry onto the bottoms of theanalysis chambers, thus immobilizing the reagents so that they do notmove outside their respective chambers during shipping. Alternatively,the reagents could be dried prior and then metered into the chambers.Once the reagents and the agitators 130 have been introduced into thecartridge 100, the lid 101 is attached, for example, by sonic welding.In one example of a cartridge for analyzing swimming-pool water, thereagents are suitable for measuring one or more of the following,preferably all: free chlorine/bromine; total chlorine; total alkalinity;pH; calcium and/or magnesium hardness (at two different ranges); copper;iron; borate; and cyanuric acid. In another example, biguanide andbiguanide shock measuring reagents are substituted for the chlorine andbromine tests, and the cyanuric acid test is omitted.

In use, a measured amount of water or other liquid to be analyzed isinjected into the filling chamber 104 through the filling port 108. Theamount may be measured by filling the filling chamber 104 until thewater reaches a visible filling mark, for example, until the boundarybetween the area of the chamber 104 furthest from the fill port 108 isfilled and at a location underneath or between lines molded on thecartridge 100. As liquid is injected in the filling chamber 104, air inthe chamber is displaced through the overflow passage 116. Othermechanisms for venting air can be provided, such as a vent port on thedistribution gallery 112. The cartridge 100 is then placed over thespindle 58, with the flat surface 60 on the spindle 58 engaging the flatside of D-shaped opening 102 in the cartridge 100.

A cover 140 is then preferably placed over cartridge 100. The cover 140may be made from an opaque or black material or suitably coated to limitand absorb stray light from the LEDs 68, 70, 72, 74, and may be made ofa strong plastic to protect the analyzer 12 if there is any failure ofthe cartridge 100. The cover 140 may have openings aligned with theanalysis chambers 120, and a D-shaped central opening that engages theflat 60 of spindle 58 so that the openings in the cover 140 remain inalignment with the analysis chambers 120. The cover 140 may be omitted.In an alternative embodiment, another provision may be made for reducingstray light. For example, the spindle 58 may be provided with a flatplate on which the cartridge 100 rests, and which has openings alignedwith the analysis chambers 120.

Once the cartridge is mounted, the lid 54 is closed, and the analyzer 12is activated, either by a control on the analyzer itself or by a commandsignal from a computer 14. The motor 62 rotates the spindle 58, whichrotates the cartridge 100 at a speed suitable for generating sufficientcentrifugal force to cause the liquid to flow outward from the fillingchamber 104 through the transfer passage 110 to the distribution gallery112. The liquid flows along the distribution gallery 112, and outward,again by centrifugal force, through the channels 114 to fill theanalysis chambers 120 and the comparison chamber 124. Any excess liquidwill pass through the whole length of the distribution gallery 112 intothe overflow chamber 126. Any excess liquid should remain in fillingchamber 104 or distribution galley 112, because the outlet of overflowpassage 116 is radially inward from the distribution galley, closer tothe center of rotation.

Once the liquid has been distributed to the analysis chambers 120, themotor 62 continues to rotate the cartridge 100. As each agitator chamber122 passes the magnets 84, 86, the agitator 130 is attracted by themagnets and moves alternately up and down within the agitator chamber122, between the positions shown in FIGS. 3A and 3B, depending on themagnet it passes. The movement of the agitator 130 causes an oscillatingcirculation of liquid within the agitator chamber 122 and its associatedanalysis chamber 120. The circulation of liquid assists in thedissolving or suspension of the reagent 121 into the liquid, andfacilitate the even mixing of the reagent 121 throughout the liquid inanalysis chamber 120.

Each reagent is preferably formulated using known techniques such thatit forms an appearance such as hue, intensity of color, or opacity thatis detectable or measurable by light, depending on the presence,absence, or concentration of the analyte that each reagent is intendedto detect. In an embodiment, different reagents 121 in the differentanalysis chambers 120 form different colors, depending on theconcentration of the analyte that each reagent is intended to detect.

Each color may be measured by the absorption of the light from one ormore of the LEDs 68, 70, 72, 74 before it reaches its respectivetransducer 76, 78, 80, 82, or alternatively, by the amount of light thatpasses through to the respective transducer. The colors may vary in hue,intensity, or both. For example, one standard reagent for measuringchlorine concentration produces a pink color that becomes darker as thechlorine concentration increases, and may be measured by the absorptionof blue light from the LED 74. For example, one standard reagent formeasuring pH varies in hue from yellow at low pH to red at high pH, andmay be measured by the absorption of light from the yellow LED 70 or thegreen LED 72. A reagent that varies in hue may also be measured by thedifference between absorptions of light from light sources of twodifferent colors.

Errors caused by variation in the intensity of the light emitted by theLEDs, and lack of transparency of the initial liquid samples, may hecorrected by measuring the light transmitted through the referencechamber 124. The light of each color transmitted by each chamber may beidentified by synchronizing the time-varying output from the transducers76, 78, 80, 82 with the timing information from the rotary encoder 64 asthe spindle 58 rotates.

In an embodiment, the processor 94 repeatedly samples the measured lightintensity data from the transducers 76, 78, 80, 82. The processor 94discards readings that do not match one of the analysis chambers 120 orthe reference chamber 124. Merely by way of example, the processor 94may sample the transducers 400 times per revolution of the cartridge100, and extract 4 readings for each analysis chamber 120 perrevolution. The readings are then averaged over several revolutions, anda matrix of 11×4 averaged readings is transmitted by the processor 94 tothe computer 14. The computer 14 is programmed with calibration data forthe set of reagents 121 in the cartridge 100, and converts the lightintensity data into concentrations of the various analytes. Programs forconverting the light intensities into analyte concentrations, includingdatabases of the characteristics of standard reagents, are commerciallyavailable and, in the interests of conciseness, need not be furtherdescribed here. The computer 14 may display the concentrations on screen20. While the analyzer is shown having a processor 94 mounted within it,it is also contemplated that all the processing may occur at thecomputer. Alternatively, the processor 94 can be programmed to provideall the analysis necessary and provide the results to the computer orother display device.

Instead, or in addition, where the liquid sample being analyzed has adesired or ideal condition (as is the case, for example, with swimmingpool water) the computer 14 may be programmed with a data file ofavailable treatments to adjust the condition. Optionally, relevantproperties of a source of the liquid sample being analyzed may also bestored on the computer 14 or input during the analysis, and the computer14 may then generate a prescription for treatments to correct anyproblem detected by the analysis.

For example, if the sample being analyzed is water from a swimming poolbeing analyzed at a pool supplies store, one important piece ofinformation is the size of the pool. If the analysis shows that thewater is outside a desirable range for one or more analytes in thespecific size pool, the computer 14 can then generate a list of specificquantities of select pool chemicals that are in stock in the store andneeded to correct the results of the analysis. Because different brandsof chemicals may come in different formulations, container sizes, andconcentrations, that typically may require at least a separate data filefor each brand.

As an example of suitable dimensions, for a water analyzing apparatusfor swimming-pool water, a cartridge as shown in FIG. 3 may beapproximately 23 mm ( 15/16 inch) in radius to the centers of theanalysis chambers, and approximately 12 mm (½ inch) high. The amount ofwater used may be from 2.7 to 2.9 ml. The cartridge may be rotated ataround 2300 rpm to distribute the water to the analysis chambers 120 andthe reference chamber 124 and to expel bubbles, and then at a maximum of4500 rpm to ensure proper transfer of the water from the filling chamberto the reaction chambers, and at 300 rpm to obtain the optimum pumpingaction from the agitators. The rotation is continued for a periodsufficient to allow the reagents to become dissolved in the water, toreact with their respective analytes, and for the color or othermeasurable optical property to develop. It is presently believed that ananalysis of swimming pool water of acceptable quality can be obtained inless than a minute from when rotation starts.

It is contemplated that the cartridge my include indicia, such as a barcode, RFID tag, or other form of information that can be read, such aswith a scanner or reader mounted in the analyzer, which determines thereagents that are stored in the cartridge being analyzed. This permitsan analyzer to be used with multiple cartridges, without the user havingto input anything. However, it is also contemplated that the user canselect the sample being analyzed (e.g., pool water, water for beerbrewing process, etc.) directly on the computer. The computer would usethe information for purposes of selecting the appropriate data file foranalyzing the sample data transmitted from the analyzer.

Referring now also to FIG. 4, an alternative embodiment of the cartridge100′ is similar to that described above except that, in place of slot128, the analysis chamber 120 and the agitator chamber 122 are separatedby a solid septum 132, with apertures 134, 136, at both ends. Thecartridge 100′ may be used in the same way as the cartridge 100. In use,movement of agitator 130 up and down within agitator chamber 122 causesliquid to flow in and out through apertures 134, 136 alternately,resulting in a reciprocating flow within analysis chamber 120. Thereciprocating flow causes turbulence within the analysis chamber 120that assists in dissolution and distribution of the reagent.

Although specific embodiments have been described, various modificationsare possible without departing from the spirit of the invention or thescope of the appended claims, and features of the different embodimentsmay be combined into one embodiment.

For example, although the agitators have been described as stainlesssteel ball bearings that are attracted to the magnets 84, 86, theagitators could instead also be magnets. If the agitators are elongatedso that they cannot rotate within their chambers, they could bemagnetically polarized so as to be repelled, instead of attracted, byone or more of magnets 84, 86. It is presently preferred to provide twomagnets 84 and 86, so that agitators are positively driven both up anddown once per revolution. However, more magnets could be provided, or insome circumstances there could be only a single magnet driving theagitators upwards, with the agitators being returned by gravity.

In the cartridges 100, 100′ shown in the drawings, the analysis chambers120 and the reference chamber 122 are evenly spaced in a circle aroundthe circumference of the cartridge. Other arrangements are possible. Forexample, there could be two concentric circles of analysis chambers.

The cartridge shown in FIG. 3 is intended to be disposable, and may befabricated by gluing or welding a generally flat lid on a molded body.However, the cartridge could instead be reusable, in which case the lidmay be removable to permit cleaning and recharging of the reagents inthe analysis chambers.

It would be possible to omit the rotary encoder 64, and use the signalfrom one or more of the LEDs and transducer pairs to provide a rotaryencoder input to the processor 94. However, because the reagents in theanalysis chambers 120 will cause the signals from the transducers 76,78, 80, 82 to vary, a dedicated encoder 64 may give more reliable, andmore easily interpreted, signals.

As shown in the drawings, the LEDs 68, 70, 72, 74, the photoelectrictransducers 76, 78, 80, 82, the magnets 84, 86, the cartridge analysischambers 120, the cartridge agitator chambers 122, and the cartridgereference chamber 124 are all centered on a single rotationalcylindrical surface centered on the axis of spindle 58. Otherarrangements are possible. For example the magnets and agitators couldbe on one cylinder, and the LEDs, analysis and reference chambers, andtransducers could be on another cylinder of different radius. One orboth of those cylindrical surfaces could instead be conical. The magnets84, 86 do not need to be exactly aligned with the agitator chambers 122,provided they are near enough to produce the desired motion of theagitators 130.

While the analyzer is shown having a processor 94 mounted within it, itis also contemplated that all the processing may occur at the computer.Alternatively, the processor 94 can be programmed to provide all theanalysis necessary and provide the results to the computer or otherdisplay device.

Furthermore, while the figures show the analyzer connected directly tothe computer, it is contemplated that the connection could be through aninternet connection, thus permitting samples to be run in the analyzerat a location that is remote from the computer than analyzes the dataand provides the results.

Accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification, as indicating the scope of theinvention.

1. A rotary analytical device comprising: a housing having a cavityformed therein, the cavity being defined by a bottom wall and at leastone side wall, the cavity having an axis; an impeller extending into thecavity and rotatable about the axis; a motor mounted within the housingand connected to the impeller, the motor adapted to rotate the impeller;at least one magnetic element in the housing at a location proximate tothe cavity and offset from the axis; at least one light source in thehousing and arranged to direct a beam of light into the cavity; and atleast one light sensor in the housing and arranged to receive light fromthe at least one light source, the sensor being sensitive to light of acolor emitted by the light source.
 2. A rotary analytical deviceaccording to claim 1, wherein there are a plurality of magnetic elementsmounted to the housing.
 3. A rotary analytical device according to claim2, wherein magnetic elements are offset at equal distances from theaxis, and spaced apart circumferentially from one another.
 4. A rotaryanalytical device according to claim 3, wherein the housing includes alid and a body portion, the lid being hinged to the body portion, thecavity being locate in the body portion and enclosed by the lid, andwherein some of the plurality of magnetic elements are mounted in orbelow the bottom wall and the remainder of the magnetic elements aremounted in the lid, the magnets in the lid not being aligned verticallywith the magnetic elements on the bottom wall such that they arecircumferentially spaced apart from each other.
 5. A rotary analyticaldevice according to claim 4, in combination with a cartridge mountableon the impeller with the cavity for being rotated by the impeller, thecartridge comprising: a cartridge housing having a central axiscoincident with the axis of the impeller; a plurality of analysischambers in the housing, the chambers being spaced apart from the axisand located circumferentially about the axis; and a magnetically movableelement located in each analysis chamber and movable within the analysischamber, the element adapted to cause the mixing of fluid in theanalysis chamber.
 6. A rotary analytical device according to claim 5,wherein the magnetic elements are positioned in the housing so as to besubstantially near the magnetically movable elements of the cartridgesuch that when the cartridge is rotated within the cavity, as themagnetically movable element passes a magnetic element, the magneticallymovable element is attracted to or repelled from the magnetic element.7. A rotary analytical device according to claim 1, wherein there are aplurality of said light sources spaced apart circumferentially from oneanother and at substantially the same radial distance from the axis ofthe cavity; and wherein there are a plurality of light sensors, eachlight sensor being sensitive to light received from one of the lightsources.
 8. A rotary analytical device according to claim 7, whereinthere are an equal number of light sources and light sensors, andwherein the device is configured such that a light sensor analyzes lightonly from a specific light source.
 9. A rotary analytical deviceaccording to claim 8, further comprising circuitry operative to measuretime-varying light intensities sensed by the plurality of sensors,associate the intensities with ones of a plurality of locations on acartridge rotating on said impeller, and generate an output responsiveto the intensities at specific ones of the locations.
 10. A rotaryanalytical device according to claim 9, wherein the output is responsiveto intensities at specific wavelengths and/or to specific variations inintensity with wavelength at the locations.
 11. The analytical cartridgeof claim 5, wherein the analysis chamber comprises a first chambersection containing the magnetically movable element and a second chambersection fluidly connected with the first chamber section, and whereinthe fluid connection between the first and second chamber sectionsincludes an axial slot that is narrower than a minimum dimension of themagnetically movable element.
 12. The analytical cartridge of claim 11,wherein the analysis chamber contains a photometric reagent, and whereinthe housing above and below the second chamber section includes aportion that is transparent to light of at least one wavelengthappropriate for photometry of the reagent.
 13. The analytical cartridgeof claim 12, further comprising at least one reference chamber without amagnetically movable element.
 14. The analytical cartridge of claim 12,comprising a distribution gallery located radially inward from andfluidly connected to the analysis chambers, the distribution galleryadapted to distribute a liquid to be analyzed to the analysis chambersthrough centrifugal force upon rotation of the cartridge about the axis.15. The analytical cartridge of claim 14, wherein the distributiongallery has an inlet for receiving the liquid to be analyzed at one end,and is connected to an overflow chamber at the other end; and whereinthe fluid connection with the analysis chambers includes a plurality ofchannels located between the inlet and the overflow chamber andextending radially from the distribution gallery, each channel connectedto an analysis chamber.
 16. The analytical cartridge of claim 13 whereinthe analysis chambers and the at least one reference chamber are evenlyspaced circumferentially about the axis, wherein the at least onereference chamber does not have a first chamber section, and wherein theoverflow chamber is larger than one of the analysis chambers, and theoverflow chamber and the at least one reference chamber together occupythe same space as two said analysis chambers.
 17. The analyticalcartridge of claim 12, wherein the magnetically movable element is aball bearing.